US President Barack Obama has ruled out "wheeling and dealing" with China and Russia over a US request to extradite former American spy agency contractor Edward Snowden.

Obama, who appeared concerned that the case would overshadow a three-country tour of Africa that he began in Senegal, also dismissed suggestions that the United States might try to intercept Snowden if he were allowed to depart Moscow by air.

"No, I'm not going to be scrambling jets to get a 29-year-old hacker," he told a news conference in Dakar, a note of disdain in his voice. Snowden turned 30 last week.

Obama said regular legal channels should suffice to handle the US request that Snowden, who left Hong Kong for Moscow, be returned. Obama said he had not yet spoken to China's President Xi Jinping or Russian President Vladimir Putin about the issue.

"I have not called President Xi personally or President Putin personally and the reason is ... number one, I shouldn't have to," Obama said sharply.

"Number two, we've got a whole lot of business that we do with China and Russia, and I'm not going to have one case of a suspect who we're trying to extradite suddenly being elevated to the point where I've got to start doing wheeling and dealing and trading on a whole host of other issues," he said.

Snowden fled the United States to Hong Kong this month after leaking details of secret US government surveillance programmes, then flew to Moscow on Sunday. He had been expected to fly on to Havana on Monday but did not board the aircraft.

The American, who faces espionage charges in the United States and has asked Ecuador for political asylum, has not been seen since his arrival in Moscow. Russian officials said he remained in a transit area at Sheremetyevo airport.

CHINA, ECUADOR HIT BACK

Snowden's case has raised tensions between the United States and both China and Russia. Yesterday, Beijing accused Washington of hypocrisy on the issue of cyber security.

Obama's remarks seemed calibrated to exert pressure without leading to lasting damage in ties with either country.

Andy Smith, director of the University of New Hampshire Survey Centre, said Obama was trying to play down the Snowden saga and minimise the impact on the United States.

"The more the administration can play it down, the more latitude they'll have in the diplomatic arena to work out a deal for him," he said.

Obama predicted there would be a made-for-TV movie about the ongoing saga, but indicated that damage to US interests was largely limited to revelations from Snowden's initial leak.

"I continue to be concerned about the other documents that he may have," Obama said. "That's part of the reason why we'd like to have Mr Snowden in custody."

Snowden's revelations of widespread snooping by the US National Security Agency in China and Hong Kong have given Beijing considerable ammunition in an area that has been a major irritant between the countries.

China's defence ministry said the US government surveillance programme known as Prism "has revealed the concerned country's true face and hypocritical behaviour". It did not name the country.

"This 'double standard' approach is not conducive to peace and security in cyber space," ministry spokesman Yang Yujun told reporters, according to state news agency Xinhua.

In Ecuador's capital Quito, the government said it was waiving preferential rights under a US trade agreement to demonstrate its principled stand on Snowden's asylum request.

In a deliberately cheeky touch from the leftist government of President Rafael Correa, Ecuador also offered a multi-million donation for human rights training in the United States.

Ecuadorean officials added that the US fugitive's case had not been processed because he had not yet reached any of its diplomatic missions.

"USEFUL" CONVERSATIONS

Obama said the United States expected all countries who were considering asylum requests for the former contractor to follow international law.

In Washington, the US State Department warned of "grave difficulties" for US-Ecuador relations if the Andean country were to grant Snowden asylum, but gave no specifics.

The White House said last week that Hong Kong's decision to let Snowden leave would hurt US-China relations. Its rhetoric on Russia has been somewhat less harsh.

Obama acknowledged that the United States did not have an extradition treaty with Russia, but he said such a treaty was not necessary to resolve all of the issues involved.

He characterised conversations between Washington and Moscow as "useful" and said the United States would continue to press.

Putin has rejected US calls to expel Snowden to the United States and said on Tuesday the fugitive should choose his destination and leave the airport as soon as possible. Ecuador has said it could take weeks to decide on his asylum request.

Washington is focused on how former Booz Allen Hamilton systems administrator Snowden gained access to National Security Agency secrets while working at a facility in Hawaii.

Obama said the leaks exposed "pretty significant vulnerabilities" at the NSA that had to be resolved.

In Baltimore, NSA Director Keith Alexander said the leaks had caused "significant and irreversible damage" and hurt the United States as well as its allies.

"I believe the irresponsible release of classified information will have a long-term detrimental impact on the intelligence community's ability to detect future attacks," Alexander told the AFCEA International Cyber Symposium.